The measurement of caloric expenditure is central to the nutritional and metabolic study of diverse conditions ranging from normal physiological responses to pathological conditions such as obesity and diabetes mellitus. A variety of techniques are available for the study of thermogenesis in man, each one providing a unique set of capabilities. At present the Energy Expenditure Core Laboratory of the Obesity Research Center at St. Luke's/Roosevelt Hospital Center of Columbia University is capable of evaluating most components of heat production in humans. In addition to specific to specific instrumentation, this laboratory has external resources capable of design, construction, and operation of calorimetry systems. A large group of investigators relies on this facility for patient studies. The proposal is aimed at the acquisition and construction of a respiratory chamber-indirect calorimeter at the Energy Expenditure Core Laboratory. The availability of this instrument will fill an important gap in our present capabilities by allowing extended (24 hour) measurement intervals and precise calculation of energy-elemental balance with associated body composition changes. In addition, the availability of this instrument will allow human studies of the relation of malnutrition to altered thermogenesis and thermoregulation. Eleven specific projects presently require or would be greatly improved by the availability of this respiratory chamber. This proposal specifies the resources available and the scientific basis for the installation of this indirect calorimetry system.